How to operate a rotary kiln

Abstract

To prevent damage to equipment on a downstream side of a rotary kiln using coal as a fuel, caused by an excessive rise of exhaust gas temperature by suppressing intrusion of a volatile component into a heating furnace on the downstream side of the rotary kiln, by reducing a volatile component of coal discharged from the rotary kiln as unburned,.SOLUTION: A rotary kiln 1 is a heating furnace to which coal C is charged, and another heating furnace is connected to the rotary kiln 1 on the downstream process side thereof. In the operation method of the rotary kiln 1, a moisture content of the coal C is 10 wt.% or more, and a pretreatment for pulverizing a particle size distribution of the coal C charged into the rotary kiln 1 is performed.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for operating a rotary kiln, and more particularly to a method for operating a rotary kiln that can be particularly preferably applied to the operation of a drying / reducing rotary kiln that performs a calcination and drying treatment of nickel oxide ore as a raw material in ferronickel smelting. [Background technology]

[0002] In smelting ferronickel, an alloy of iron and nickel, nickel oxide ore is used as a raw material. It is first partially reduced in a rotary kiln for drying and reduction, while removing moisture, and then charged into an electric furnace for melting and reduction.

[0003] In the above-mentioned calcination and drying process carried out using a rotary kiln, in addition to heavy oil burned by a burner provided at the discharge end of the rotary kiln, coal, which is also used as a reducing agent, is used as a heat source. In order to reduce the amount of expensive heavy oil used among these fuels, an operating method is also carried out in which coal, which serves as a reducing agent, is charged into the middle of the rotary kiln (see Patent Document 1). By charging coal into the middle of the rotary kiln, the coal can be supplied to the high-temperature part of the rotary kiln, and the volatile matter contained in the coal can be burned efficiently.

[0004] However, even when the above-mentioned charging method is adopted, unburned volatile matter still remains in the coal discharged from the rotary kiln. The coal containing the volatile matter is introduced into an electric furnace installed downstream of the rotary kiln. The combustion of the unnecessary volatile matter causes the temperature of the exhaust gas discharged from the electric furnace to rise excessively, causing damage to the exhaust gas flue.

[0005] For example, the exhaust gas temperature can be reduced by reducing the output of an electric furnace. However, reducing the output of the electric furnace reduces the productivity of the entire process. Therefore, there has been a demand for a means to avoid the increase in the exhaust gas temperature without reducing the output of the electric furnace in actual operation. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2014-141719 A Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention aims to reduce the volatile matter of coal that is discharged from a rotary kiln that uses coal as fuel, thereby suppressing the intrusion of the volatile matter into other heating furnaces in the downstream process, and preventing damage to downstream flue equipment, etc., caused by an excessive increase in the temperature of the exhaust gas discharged from the other heating furnace. [Means for solving the problem]

[0008] The present inventors have come to the conclusion that the above-mentioned problems can be solved by optimizing the particle size distribution of coal fed into a rotary kiln, and have completed the present invention. Specifically, the present invention provides the following.

[0009] (1) A method for operating a rotary kiln, which is a heating furnace into which coal is fed and which is further connected to another heating furnace on the downstream side, wherein the moisture content of the coal is 10% by weight or more, and a pretreatment is performed to refine the particle size distribution of the coal fed into the rotary kiln.

[0010] According to the rotary kiln operation method (1), it is possible to reduce the amount of volatile matter in the coal discharged from the rotary kiln without burning. This makes it possible to suppress the unnecessary intrusion of volatile matter into other heating furnaces on the downstream side. This makes it possible to prevent an unnecessary increase in the temperature of the exhaust gas discharged from the other heating furnaces on the downstream side while maintaining the processing efficiency of the other heating furnaces on the downstream side.

[0011] (2) The method for operating a rotary kiln according to (1), wherein the pretreatment is performed to set the particle size distribution of the coal before it is charged into the rotary kiln so that the proportion of particles having a particle size of 10 mm or less is 95% or more.

[0012] According to the rotary kiln operation method of (2), the above-mentioned effects achieved by the rotary kiln operation method described in (1) can be obtained more reliably and stably.

[0013] (3) The method for operating a rotary kiln according to (1) or (2), wherein the pretreatment is carried out using a roll crusher.

[0014] According to the rotary kiln operation method of (3), the particle size distribution of coal can be stably maintained within a predetermined range with a simple operation, and thus the above-mentioned effects of the rotary kiln operation method described in (1) or (2) can be easily and stably enjoyed.

[0015] (4) The method for operating a rotary kiln according to any one of (1) to (3), wherein the rotary kiln is a drying / reduction rotary kiln for performing a partial reduction step of a raw material nickel oxide ore in ferronickel smelting.

[0016] According to the rotary kiln operation method of (4), the above-mentioned effects of the rotary kiln operation method described in any one of (1) to (3) can be enjoyed, and it is possible to contribute to improving productivity in the production of ferronickel smelting.

[0017] (5) A method for operating a rotary kiln according to any one of (1) to (4), wherein the other heating furnace is an electric furnace.

[0018] (5) According to the rotary kiln operating method, it is possible to prevent damage to each piece of equipment caused by an excessive rise in temperature of the exhaust gas discharged from the electric furnace, which has been a problem in industrial facilities where the firing and drying process using a rotary kiln and the reduction and melting process using an electric furnace are performed consecutively. Effect of the Invention

[0019] According to the method for operating a rotary kiln of the present invention, in a rotary kiln that uses coal as fuel, it is possible to reduce the amount of volatile matter in the coal discharged from the rotary kiln without burning it, thereby suppressing the intrusion of volatile matter into other heating furnaces in the downstream process, and preventing damage to downstream flue equipment, etc., caused by an excessive increase in the temperature of the exhaust gas discharged from the other heating furnaces. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a schematic diagram showing an example of an embodiment in which the rotary kiln operating method of the present invention is carried out in a drying / reducing rotary kiln used in the entire process of ferronickel smelting. [Diagram 2] FIG. 1 is a cross-sectional view showing another example of a rotary kiln in which the present invention can be implemented in a preferred embodiment, the rotary kiln having a scoop feeder for feeding coal. [Diagram 3] FIG. 1 is an explanatory diagram of the structure of a roll crusher that can be preferably used as a crusher for carrying out the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Specific embodiments of the "rotary kiln operation method" of the present invention will be described below. Note that the present invention is not limited to the following embodiments, and can be embodied in other forms and modes than those described below without departing from the gist of the present invention.

[0022] <The entire process of ferro-nickel smelting> The rotary kiln operation method of the present invention (hereinafter also simply referred to as "rotary kiln operation method") is an operation method particularly preferably implemented in a rotary kiln (drying / reducing rotary kiln) that performs a partial reduction process (partial reduction process) in the "overall ferronickel smelting process". However, the technical scope of the "rotary kiln operation method" is not limited to implementation in such a specific rotary kiln. This "rotary kiln operation method" is a heating furnace that burns coal, and is a process that can be widely implemented in various rotary kilns that are further connected to other heating furnaces on the downstream process side.

[0023] In this specification, the phrase "a rotary kiln further connected to another heating furnace on the downstream process side" means that the rotary kiln, which is a heating furnace installed on the upstream process side, is installed so that both facilities operate in conjunction with each other in a manner that high-temperature discharge from the rotary kiln, which is a heating furnace installed on the upstream process side, is fed into the "other heating furnace" installed on the downstream process side. For example, even if the rotary kiln and the other heating furnace operating in conjunction with each other in the above manner are connected via a transport device such as a belt conveyor, this is naturally a "rotary kiln further connected to another heating furnace on the downstream process side" and is within the scope of the present invention.

[0024] The above-mentioned "overall process of ferronickel smelting" is a process that uses nickel oxide ore (hereinafter also simply referred to as "ore") as a raw material and at least a partial reduction step and a smelting reduction step are essential steps. This process can produce ferronickel with a nickel content of about 20% by weight. In this process, if necessary, a drying step preceding the partial reduction step and a desulfurization step following the smelting reduction step are also carried out.

[0025] [Partial reduction process] The partial reduction process is a process in which moisture (adherent water, crystal moisture) in the ore is completely removed and partially reduced ore (hereinafter also referred to as "calcined ore"). In the partial reduction process, a reducing agent (coal) and, if necessary, a melting agent are further added to the ore that has been dried to a moisture content of about 20% by weight, and these are put into a rotary kill for drying and reduction, and calcined at a temperature of about 800°C to 900°C to obtain calcined ore.

[0026] By carrying out this partial reduction step using the "rotary kiln operating method" of the present invention, it is possible to suppress the intrusion of coal volatile matter into the electric furnace in which the subsequent melting reduction step is carried out, and to prevent damage to the flue equipment, etc., which would otherwise be caused by an excessive increase in the temperature of the exhaust gas discharged from the electric furnace.

[0027] [Melting reduction process] The melting reduction process is a process in which the calcined ore produced in the partial reduction process is put into an electric furnace and melted and reduced in the furnace to produce ferronickel (metal) and slag. The ferronickel molten body produced in this process is mainly composed of iron and contains nickel at a grade of about 16% by weight to 25% by weight depending on the set amount of carbonaceous reducing agent. Although the electric furnace is not shown in the figure, a specific example of an electric furnace that performs melting reduction is the well-known "three-phase AC electrode type circular electric furnace."

[0028] <How to operate a rotary kiln> As described above, the "rotary kiln operating method" is a method that can be preferably implemented as a method for operating a rotary kiln for drying and reduction, which performs a partial reduction step in the "overall process of ferronickel smelting".

[0029] [coal] In addition, the "rotary kiln operating method" is an operating method that is effective when coal containing a certain amount of moisture or more, specifically coal with a moisture content of 10% by weight or more, is used as fuel to be fed into the rotary kiln.

[0030] Here, the coal used as a reducing agent in a ferronickel smelting plant is usually stored outdoors, including during transportation, and is generally charged into a rotary kiln with a moisture content of 10% by weight or more. Therefore, in the "rotary kiln operation method", coal that is usually used in ferronickel smelting can be used as is in many cases. Furthermore, even if the coal is in a dry state with a moisture content of less than 10% by mass, it can be used as coal for carrying out the method of the present invention by carrying out some kind of humidification treatment so that the moisture content is 10% by weight or more by the stage immediately after pretreatment.

[0031] The composition of coal that can be suitably used in the "rotary kiln operation method" may have a moisture content of 10% by weight or more, and preferably has a moisture content of 10% by weight to 15% by weight, a volatile content of 25% by weight to 40% by weight, carbon in the coal after the volatile content has been removed from the coal (hereinafter referred to as "fixed carbon") of 40% by weight to 60% by weight, and an ash content of 10% by weight to 20% by weight. In this specification, the "volatile content contained in coal" refers to a value measured by industrial analysis according to the JIS standard, and specifically refers to a value obtained by subtracting the moisture content quantified at the same time from the mass loss rate when a sample dried at room temperature in air is heated at 900°C for 7 minutes without contact with air.

[0032] [Crusher and coal pretreatment] Fig. 1 is a schematic diagram showing an example of an embodiment in which the "rotary kiln operating method" of the present invention is carried out in a drying / reducing rotary kiln used in the above-mentioned "overall process of ferronickel smelting". The "rotary kiln operating method" is an operating method characterized mainly by carrying out, as an essential step, a pretreatment process in which coal containing a certain amount of moisture or more is pulverized so that the particle size distribution falls within a predetermined range before being charged into the rotary kiln.

[0033] As shown in FIG. 1, in the "method of operating a rotary kiln", coal to be fed into a rotary kiln 1 is pulverized by pretreatment using a pulverizer. The pulverizer used in the pretreatment to pulverize the coal is not particularly limited, and various known pulverizers, specifically jaw crushers, gyratory pulverizers, disk pulverizers, etc., can be appropriately selected and used. However, in the "method of operating a rotary kiln", it is preferable to use a roll crusher 2 among the above-mentioned various devices. As shown in FIG. 3, a roll crusher is a pulverizer that pulverizes the material to be pulverized by passing it between two rolls 21A and 21B that rotate in opposite directions to each other, by compression.

[0034] The roll crusher 2 has two rolls, and the crushing teeth 22 extending in the longitudinal direction of the roll 21A are arranged on the outer surface of one of the rolls, roll 21A, at equal intervals in the circumferential direction of the roll surface. By adjusting the distance between the central axes of the two rolls 21A and 21B, it is possible to adjust the gap C1 between the roll surfaces of the two opposing rolls 21A and 21B, and the gap C2 between the crushing teeth 22 provided on the roll 21A and the roll surface of the roll 21B facing the crushing teeth 22. As a preferred example, the outer diameter of the roll is 760 mm, and the height of the crushing teeth is 7 mm.

[0035] For example, when the height of the crushing teeth 22 of the roll crusher 2 is 7 mm, the gap C2 between the crushing teeth 22 and the roll surface of the roll 21B facing the crushing teeth 22 can be adjusted to 2 mm by adjusting the distance between the central axes of the two rolls so that the gap C1 between each roll surface of the two rolls 21A, 21B is 9 mm. When coal C is charged into the roll crusher 2 with the gap adjusted to the above size, the coal C passing through the area where the crushing teeth 22 are arranged is crushed to a size that can pass through a 2 mm gap, and the coal passing through the area where the crushing teeth 22 are not arranged is crushed to a size that can pass through a 9 mm gap, becoming finely divided coal c.

[0036] The roll crusher 2 can adjust the size of the gap C1 between the roll surfaces of the two rolls 21A and 21B, the crushing teeth 22 provided on the roll 21A, and the size of the gap C2 between the roll surface of the roll 21B facing the crushing teeth 22. By optimizing these gaps, the coal C can be crushed into finely granulated coal c having a desired particle size distribution. The roll crusher 2 may have a mechanism for moving the rolls in a direction in which the distance between the central axes is separated from each other, thereby enlarging the gap C1 between the two opposing rolls 21A and 21B and the gap C2 between the crushing teeth 22 and the roll 21B facing the crushing teeth 22.

[0037] By using the roll crusher 2 as the crusher, for example, the size of the gap C1 and the gap C2 can be adjusted so that the ratio of coal particles having a particle size of 10 mm or less after crushing exceeds a desired ratio. Here, coal having a particle size of 10 mm or less means coal that can pass through a sieve with an opening of 10 mm. To be more specific, for example, when the outer diameter of the two rolls 21A and 21B is 760 mm and the height of the crushing teeth is 7 mm, the size of the gap C2 can be narrowed to 4 mm, 3 mm, and 2 mm, so that the ratio of coal particles having a particle size of 10 mm or less in the crushed coal c can be increased to 70.4%, 74.5%, and 97.3%. In other words, the ratio of coal that can pass through a sieve with an opening of 10 mm can be increased to 70.4%, 74.5%, and 97.3%.

[0038] In the above pretreatment, it is preferable to crush the coal before feeding it into the rotary kiln so that the proportion of coal particles with a particle size of 10 mm or less is 70% or more, and more preferably so that the proportion is 95% or more. By increasing the proportion of coal particles with a particle size of 10 mm or less in this manner, it is possible to suppress the intrusion of volatile matter into the electric furnace and suppress the rise in temperature of the exhaust gas discharged from the electric furnace. In this specification, the particle size distribution (%) of coal refers to the relative amount (mass ratio) of coal in each particle size range.

[0039] For example, when dried coal with a moisture content of about 5% by weight is crushed and refined to the particle size distribution described above, there is a risk of dust generation after crushing and before it is fed into the rotary kiln. However, in the "rotary kiln operation method" of the present invention, the moisture content of the coal is limited to 10% by weight or more, thereby avoiding the risk of dust generation due to fine particle size while effectively combusting the volatile matter contained in the coal fed into the rotary kiln 1, thereby reducing the proportion of volatile matter contained in the coal discharged from the rotary kiln 1.

[0040] [Transporting and feeding coal into the rotary kiln] As shown in Fig. 1, the coal c pulverized through the above-mentioned "pretreatment" is stored in a hopper 4 via a pipe conveyor 3. Then, a fixed amount of granular coal c is discharged from the hopper 4 and fed into the rotary kiln 1 from a coal supply port 12 via a coal feeding conveyor 5. The amount of granular coal c fed into the rotary kiln 1 can be appropriately controlled by adjusting the fixed amount discharged by the hopper 4 as necessary.

[0041] Furthermore, when carrying out the "rotary kiln operating method" of the present invention, it is preferable that the coal transport path to the rotary kiln 1 is constructed with a pipe conveyor 3. By adopting the pipe conveyor 3, which has an enclosed structure and is suitable for transporting powdery or other dust-generating materials, it is possible to more reliably prevent the coal that has been finely ground by the above-mentioned "pre-treatment" from scattering into the surrounding area due to dust generation.

[0042] [Rotary kiln] As shown in Fig. 1, the rotary kiln 1 is a large cylindrical rotary heating furnace. The rotary kiln 1 is inclined downward from its charging end 11 toward its discharge end 13. In the rotary kiln 1, the raw material dry ore is charged from the charging end 11, and the dry ore moves inside the rotating body toward the discharge end 13. In the rotary kiln 1, a burner 14 for heating, such as a heavy oil burner, is usually installed on the discharge end 13 side, and the combustion heat of the fossil fuel fired by the burner 14 flows in the opposite direction to the dry ore, thereby countercurrent heating the dry ore.

[0043] The temperature inside the rotary kiln 1 is not particularly limited, but it is preferable to maintain the ore temperature at the discharge end 13 at about 700°C to 900°C and the exhaust gas temperature at the charging end 11 at about 250°C to 400°C. By maintaining the above temperatures at or above the respective lower limit temperatures, the volatile matter and fixed carbon in the charged coal can be sufficiently combusted. Furthermore, by maintaining the above temperatures at or below the respective upper limit temperatures, the occurrence of scum on the inner wall of the rotary kiln 1 can be prevented.

[0044] The rotation speed of the rotary kiln 1 is not particularly limited, but is preferably about 0.5 rpm or more and 1.5 rpm or less. If the rotation speed of the rotary kiln 1 is less than 0.5 rpm, the stirring force inside the rotary kiln 1 is weak, and the charged coal, while buried in the dry ore as the raw material, slowly slides in the circumferential direction and moves little by little from the charging end 11 side to the discharge end 13 side. In such a case, there is a concern that the contact between the coal surface and the air in the rotary kiln 1 becomes insufficient, making it difficult to burn the volatile matter and fixed carbon in the charged coal. On the other hand, if the rotation speed of the rotary kiln exceeds 1.5 rpm, the stirring force inside the rotary kiln 1 becomes strong, and the raw material dry ore charged in the rotary kiln 1 is blown up inside the rotary kiln 1 and discharged from the charging end 11 as dust together with the exhaust gas, which may reduce the recovery rate of the calcined ore obtained from the discharge end 13.

[0045] The size of the rotary kiln 1 is not particularly limited, but for drying and reduction in ferronickel smelting, a rotary kiln with an inner diameter of about 4.5 m to 6.5 m and a total length of about 100 m to 150 m is preferably used. With a rotary kiln with an inner diameter of less than 4.5 m or a total length of less than 100 m, it becomes difficult to ensure sufficient time required for drying and partially reducing the ore in the rotary kiln, and there is a concern that effective treatment cannot be performed. On the other hand, with a rotary kiln with an inner diameter of more than 6.5 m or a total length of more than 150 m, the capital investment for installing the rotary kiln and the cost for maintaining it increase, which is undesirable from the viewpoint of economic efficiency.

[0046] Fig. 2 is a cross-sectional view of another example of a rotary kiln in which the present invention can be implemented in a preferred embodiment, the rotary kiln having a scoop feeder for feeding coal. The scoop feeder is provided at a position midway in the direction of movement of the dried ore (the longitudinal direction of the rotary kiln body) in the rotary kiln 1A. As shown in Fig. 2, the rotary kiln 1A is composed of a rotating body part 15 and an outer shell 16 that covers the body part 15, and a scoop feeder 17 is provided at a predetermined position on the body part 15.

[0047] In a rotary kiln 1A having a scoop feeder, dried ore o as a raw material is charged into a body 15, and the dried ore o moves from the charging end 11 to the discharge end 13 as the body 15 rotates. In this rotary kiln 1A, a space 16R is formed by the body 15 and an outer shell 16, and coal c is charged into the space 16R through a coal supply port 12A provided in the outer shell 16.

[0048] The scoop feeder 17 is formed of, for example, an L-shaped pipe, scoops up coal with a tip 171 having an L-shaped curved portion, passes the scooped coal through a pipe constituting an L-shaped straight portion 172, and supplies the coal to the inside of the body portion 15. More specifically, the scoop feeder 17 is fixed to the body portion 15 at a predetermined location, and the tip 171 having the L-shaped curved portion is located in the space portion 16R formed by the body portion 15 and the outer shell 16. In this scoop feeder 17, as the body portion 15 to which the scoop feeder 17 is fixed rotates, the coal charged in the space portion 16R is scooped up through the tip 171 and taken into the scoop feeder 17. When the scoop feeder 17 is positioned at the upper part of the body section 15 as the body section 15 rotates, the coal taken into the scoop feeder 17 passes through the pipe that constitutes the L-shaped straight section 172 due to the action of gravity and is supplied to the inside of the body section 15.

[0049] In the rotary kiln 1 (1A), the location of the coal supply port 12 (12A) in the direction of movement of the dried ore (longitudinal direction of the rotary kiln body) is preferably directly above or in the vicinity of the position where the temperature inside the rotary kiln body is between 900° C. and 1200° C. By feeding coal into the rotary kiln 1A from this position, the volatile matter and fixed carbon in the coal can be efficiently combusted.

[0050] Furthermore, among the above positions, it is more preferable to install the coal supply port 12 (12A) at a position that is 2 / 10 of the total length of the rotary kiln from the discharge end 13 rather than 5 / 10 of the total length of the rotary kiln from the discharge end 13. If the position for charging coal is closer to the discharge end 13 than 2 / 10 of the total length of the rotary kiln from the discharge end 13, the residence time of the charged coal in the rotary kiln 1 will be shorter, and there will not be enough time for the coal to heat up, resulting in insufficient heating, and there is a concern that it will be difficult to burn the volatile matter and fixed carbon in the coal. On the other hand, if the coal is charged at a position closer to the charging end 11 than "a position 5 / 10 of the total length of the rotary kiln from the discharge end 13," the coal will be charged into a lower temperature part of the rotary kiln 1, and the coal will be dispersed in the ore layer from which moisture has not been completely removed, and the surface of the coal will be covered with ore containing moisture. As a result, even if the temperature of the coal increases as it moves toward the discharge end 13, the coal will not be able to come into sufficient contact with the air, and there is a concern that it will be difficult to burn the volatile matter and fixed carbon in the coal. EXAMPLES

[0051] The present invention will be described in more detail below by showing examples of test operations, but the present invention is not limited to the following examples.

[0052] [Example 1] In ferronickel smelting, a rotary kiln (rotary kiln for drying and reduction) with an inner diameter of 4.8 m and a length of 105 m was used to perform a calcination and drying process on dried ore. Coal was fed into the rotary kiln, which was rotating at a rotation speed of 1.5 rpm, via a scoop feeder installed at a position 2 / 10 of the total length of the rotary kiln body from the discharge end. Here, the particle size distribution of the coal was adjusted as follows. First, in a roll crusher having a pair of rolls with an outer diameter of 760 mm, the gap between the crushing teeth (height 7 mm) installed on one roll and the roll surface of the other roll was adjusted to 2 mm, the rolls were rotated at a speed of 110 rpm, and coal (moisture content 15% by weight) having the fluidity distribution shown in Table 1 below was charged and crushed.

[0053] A sample was taken from the crushed coal and sieved through a sieve with 10 mm openings to investigate the particle size distribution of the crushed coal. It was found that 97.3% of the coal had a particle size of 10 mm or less (see Table 2).

[0054] The obtained coal was then transported to a scoop feeder provided at the center of the rotary kiln in the longitudinal direction by using an apron feeder, and fed into the rotary kiln rotating at 1.5 rpm at a feed rate of 3.6 t / h. The temperature inside the rotary kiln at this position was 1200°C.

[0055] After the drying and reduction process of the dried ore was carried out as described above to produce calcined ore, it was charged into an electric furnace together with coal containing unburned volatile matter, and the calcined ore was reduced and melted to produce ferronickel by inputting 500 kwh / dry-ton of electricity. At this time, the temperature of the exhaust gas discharged from the electric furnace was measured at the entrance of the exhaust gas flue and was 812°C (see Table 2).

[0056] [Example 2] A test was conducted in the same manner as in Example 1, except that the gap between the grinding teeth (height 7 mm) provided on one roll and the other roll was adjusted to 3 mm. As a result, the particle size distribution of the coal obtained by grinding and the temperature of the exhaust gas discharged from the electric furnace were as shown in Table 2 below.

[0057] [Example 3] Except for adjusting the gap between the grinding teeth (height 7 mm) provided on one roll and the other roll to 4 mm, the same procedure as in Example 1 was followed. As a result, the particle size distribution of the pulverized coal and the temperature of the exhaust gas discharged from the electric furnace were as shown in Table 2 below.

[0058] [Table 1]

[0059] [Table 2]

[0060] From the results shown in Table 2, it can be seen that by refining the coal fed into the rotary kiln, the volatile matter contained in the coal discharged from the rotary kiln can be reduced, thereby suppressing the rise in temperature of the exhaust gas discharged from the electric furnace. In particular, it can be seen that in Example 1, the rise in temperature of the exhaust gas can be suppressed by 48°C compared to Example 2, and by 86°C compared to Example 3. In this way, it was confirmed that the method of operating a rotary kiln of the present invention can effectively combust volatile matter in the rotary kiln and suppress the rise in temperature of the exhaust gas discharged from the electric furnace. [Explanation of symbols]

[0061] 1. Rotary Kiln 11 Charging end 12, 12A Coal supply port 13 Discharge end 14 Burner 15 Body 16 Outer shell 16R Space 17 Scoop Feeder 171 Tip 172 Straight section 2. Roll Crusher 21(21A, 21B) Roll 22 Crushed teeth 3 Pipe conveyor 4. Hopper 5 Coal throwing conveyor

Claims

1. A method for operating a rotary kiln, which is a heating furnace into which coal is fed and in which another heating furnace is further connected to a downstream process side, comprising the steps of: The moisture content of the coal is 10% by weight or more, A method for operating a rotary kiln, comprising: performing pretreatment to reduce the particle size distribution of the coal to be charged into the rotary kiln using a roll crusher, thereby making the proportion of particles with particle sizes of 10 mm or less 95% or more of the coal.

2. The rotary kiln is a rotary kiln that dries and partially reduces the raw material nickel oxide ore in ferronickel smelting. A method for operating a rotary kiln according to claim 1.

3. The other heating furnace is an electric furnace. A method for operating a rotary kiln according to claim 1 or 2.

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